Model, Cast, And Die Materials
Question 1. Classify die materials. Give ideal requirements for die materials, advantages and disadvantages of each die material.
Answer:
Material that is used to prepare dies, cast and models are known as die materials.
Die: A positive replica of a single tooth is described as a “Die”.
Read And Learn More: Dental Materials Question And Answers
Types of Die Materials
- Gypsum:
- Type IV: dental stone.
- Type V: dental stone, high strength, high expansion.
- Type VI: dental stone and lignosulphonates.
- Metal and metal-coated dies:
- Electroformed
- Sprayed metal
- Amalgam.
- Polymers:
- Metal or inorganic filed resins.
- Epoxy.
- Cement: Silicophosphate or polyacrylic acid bonded cement
- Refractory materials:
- Investments and divestment.
Ideal Requirements of Die Materials:
- An ideal requirement of die materials should be:
- It should be dimensionally stable and accurate.
- It should have high strength, high abrasion resistance, and toughness to allow burnishing of foil and resist breakage.
- It should have a smooth surface.
- It should be able to reproduce all fine details in the impression.
- It should be compatible with all impression materials.
- It should have color contrast with wax, porcelain, and alloys.
- It is easy to manipulate and quick to fabricate.
- It should be non-injurious to health by touch or inhalation.
- It should be economical.
Advantages And Disadvantages Of Each Die Materials: Improved Dental Stone or Die Stone:
- Advantage Of Each Die Materials:
- Good strength
- Minimal shrinkage
- Easy manipulation
- Good working time
- Set quickly
- Compatible with impression materials
- Has a smooth, hard surface that can be easily trimmed
- Has good color contrast
- Is economic.
- Disadvantages Of Each Die Materials:
- Britte
- Not as abrasion-resistant as the epoxy and electroformed dies.
- Edges and occlusal surfaces may be rubbed off
Electroformed Die Materials: Electrodeposition of copper and silver on the impression gives a hard metallic surface to the cast.
- Advantages of Electroformed Die Materials:
- Dimensional accuracy
- Hard and abrasion-resistant
- Imparts a smooth surface to the wax pattern in contact
- Not very expensive
- Better marginal definition
- Does not absorb oil or water
- Prevents cuspal wear due to repeated contact with the opposing cast.
- Disadvantages of Electroformed Die Materials:
- Difficult to trim
- Silver bath—a health hazard
- Not compatible with all impression materials
- Color contrast is not as good as dying stone
- Adaptations of wax are not as good as the die stone, the pattern tends to lift from the margins.
Epoxy Resin Die Materials: They are most effective with rubber impression materials.
- Advantages of Epoxy Resin Die Materials:
- Tougher and more abrasion-resistant than die stone.
- Disadvantages of Epoxy Resin Die Materials:
- Slight shrinkage
- Viscous, does not flow readily.
- The setting may take up to 24 hours.
Divestment: This is a combination of die materials and investing medium.
- Advantages of Divestment
- It is a highly accurate technique for conventional gold alloys, especially for extra coronal preparations.
- In this technique, the removal of wax patterns from the die is not required.
- Thus, the possibility of distortion of the wax pattern during removal from the die or during the setting of the investment is minimized.
- Disadvantages of Divestment
- Polymers: They shrink during polymerization and so tend to produce an undersized die.
- Cement: All cement shrinks slightly exhibits brittleness and have a tendency to crack due to dehydration.
- Metal: Sprayed die: The bismuth-tin alloy is rather soft, care is needed to prevent abrasion of the die.
Question 2. Write a short note on the electroformed copper die.
Answer:
Electrodeposition of copper on the impressions gives a hard metallic surface to the cast/dies.
Advantages of Electroformed Dies:
- Dimensional accuracy
- Hard and abrasion-resistant
- Imparts a smooth surface to the wax pattern in contact
- Not very expensive
- Better marginal definition
- Does not absorb oil/water
- Prevents cuspal wear due to repeated contact with the opposing cast.
Disadvantages of Electroformed Dies:
- Difficult to trim
- Silver bath—a health hazard
- Not compatible with all impression materials
- Color contrast is not as good as dying stone
- Adaptation of wax is not as good as to the die stone, patterns tend to lift from margins.
Electroforming:
Copper electroplating is used only with rigid compound impressions. The impression is coated with copper or graphite which acts as a cathode. Anode is formed by pure copper metal.
Here, the electrolyte consists of an acidic solution of copper sulfate along with organic constituents to increase the hardness of the deposited metal. As elastomeric impression materials are not stable in an acidic solution, their copper plating cannot be done.
Question 3. Write a short note on the die and die materials.
Or
Write a brief on die materials.
Or
Write a short note on dies. (Mar 2001, 6 Marks)
Or
Classify die materials.
Or
Write in brief on die and die materials.
Answer:
Die is a positive replica of a prepared tooth or teeth in a suitable hard substance on which inlay, crown, and other restorations are made.
Ideal Requirements of Die Material:
An ideal die material should be:
- It should be dimensionally stable and accurate.
- It should have high strength, high abrasion resistance, and toughness to allow burnishing of foil and resist breakage.
- It should have a smooth surface.
- It should be able to reproduce all fine details in the impression.
- It should be compatible with all impression materials.
- It should have color contrast with wax, porcelain, and alloys.
- It is easy to manipulate and quick to fabricate.
- It should be non-injurious to health by touch or inhalation.
- It should be economical.
Types/Classification of Die Materials;
- Gypsum:
- Type IV: dental stone.
- Type V: dental stone, high strength, high expansion.
- Type V: dental stone and lignosulphonates.
- Metal and metal-coated dies:
- Electroformed
- Sprayed metal
- Amalgam.
- Polymers:
- Metal or inorganic filed resins.
- Epoxy.
- Types of cement: Silicophosphate or polyacrylic acid bonded cement.
- Ceramic or Refractory Materials: Investments and Divestment.
Description of Die Materials:
Type IV and Type V Gypsum Materials:
- Type IV and type V gypsum materials are very commonly used materials for the fabrication of dental dies. The properties of these materials provide an economical and ease of usage.
The following are the advantages of gypsum die materials:
- Lead to the accurate reproduction of fine details
- They provide relative dimensional accuracy and stability
- Good color contrast with impression material and casting waxes
- These materials are inexpensive and easy to use.
Amalgam:
Silver-tin amalgam or copper amalgam can be packed into compatible impressions, i.e. rigid impression materials such as compound to produce a hard die with fine details and sharp margins.
But this has a disadvantage, i.e. there is potential mercury toxicity. Amalgam needs rigid impression materials, and it also takes a longer time to get hardened into set mass. Its high thermal conductivity leads to cooling of the wax causing distortion of the wax pattern.
Metallic: Such dies may be produced either by direct spraying or electroplating the impression.
Metal-sprayed Dies:
Low-fusing metal alloys, i.e. bismuth-tin alloy having a melting point of l38°C can be directly sprayed on the compatible impression which creates a shell of metal in which dental stone can be filed.
Bismuth-tin alloy has the disadvantage of being soft with poor abrasion resistance. Metals and alloys can be melted with oxyacetylene or another flame. This method applies to elastomers and with care to impression compounds.
Electroplated Dies:
- The surface of the impression is made electroconvulsive by depositing file metal or graphite with the help of a camel hairbrush, this process is called metalizing.
- The coated impression becomes the cathode or the negative electrode.
- Here anode or the positive electrode is formed by the pure metal.
- The electrolyte is either an acid solution or an alkaline solution.
- Now a low voltage direct current (DC) of 5 to 50 mA/cm2 is passed for 10 hours which leads to slow dissolution of the anode with the movement of metallic ions from the anode to the cathode.
- As a shell of metal is formed, the rest of the impression is poured with dental or die stone.
- Metals commonly used for electroplating are copper or silver.
Polymers and Filled Polymers:
Acrylic as well as epoxy resins, polyesters, and epimines with ceramic or metallic filers can be used to produce dies with good abrasive resistance. The autopolymerizing reaction of these materials has inherent disadvantage of shrinkage leading to inaccuracy in the die produced.
Epoxy Resin Die Materials:
- Dies manufactured from epoxy resin or polyurethane has high strength and abrasion resistance as compared to die stone.
- Epoxy resin dies are also compatible with polyether and polyvinyl siloxane impression materials but they are not compatible with hydrocolloid impression materials since water present leads to the retardation of the polymerization of resin.
- Main disadvantage of these materials is their polymerization shrinkage which is about 0.1-0.3%. So this means they are not dimensionally stable.
- Shrinkage can be reduced to a larger extent by using either a centrifugal machine or auto mixing system.
Silicophosphate Cement:
Silicophosphate cement produces a hard die as compared to gypsum products but has higher shrinkage because of loss of water. Cement may shrink and become brittle with a tendency to crack due to dehydration affecting the accuracy of the die.
Ceramic Die Materials:
Ceramic slurry (powder and liquid) is mixed to a putt-like consistency and packed into the impression of the prepared tooth. Now the fabrication is removed from the impression after an hour and fired at 600°C for 8 minutes which produces a hard strong die. These ceramic dies are used to fabricate porcelain restorations.
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